Test Method C721, for Average Particle Size of Alumina and Silica Powders by Air Permeability, was withdrawn several years ago, mostly due to no one being available to review or revise it. A new, likely more precise, instrument that uses this technique is now commercially available: the Hazard Evaluation Laboratorys Sub-Sieve AutoSizer (HEL SAS). The Fisher Sub-Sieve Sizer (FSSS), originally used in this test method, is no longer available, nor is it supported with parts and service. Therefore, Standard C721 is being reinstated and revised to include the new instrument and indicate the lack of availability of the older instrument. Since it is likely that the older instrument is still being used in the ceramic whitewares industry, as well as in other industries, updated procedures for its use are still included in this revision, along with procedures for the use of the new instrument.
Ballot Item Approved as C721-2014 and Pending Publication